The present disclosure relates to a digital hydraulic valve stage having a sub-digit accuracy function and in particular a digital hydraulic valve.
A consumer is controlled in a digital hydraulic valve stage by means of one or a plurality of parallel arrangement(s) of one or a plurality of switching valve(s). One or a plurality of proportional valve(s) is/are typically replaced by this/these arrangement(s). A parallel arrangement of this type of a plurality of switching valves is described by the relevant scientific world as a digital hydraulic valve.
The individual switching valves of the digital hydraulic valve are typically characterized by two switching positions, namely open and closed. Accordingly, the through-flow of a digital hydraulic valve of this type that can be achieved thereby is a result approximately of the total of the (individual) through-flows of the currently open individual switching valves (also referred to as individual valves). Different magnitudes of through-flow can be achieved by selectively opening and closing the individual valves, which through-flow follow, one after the other, a specific characteristic curve of the digital hydraulic valve as illustrated in the attached FIG. 1B.
FIG. 1B illustrates the (stepped) correcting variables/through-flow characteristic curve of a digital hydraulic valve that is typically achieved. By way of comparison, FIG. 1A likewise illustrates a corresponding (continuous) characteristic curve of an analog proportional valve. The maximum number of through-flow openings illustrated in FIG. 1B and/or the self adjusting values for the respective difference through-flow openings dQ in the case of a digital hydraulic valve is also described as quantization. However, this quantization represents a disadvantageous limitation for control procedures, since the correcting variables/through-flow characteristic curve of a digital hydraulic valve always represents only a more or less close approximation to the continuous characteristic curve of a proportional valve. The limitation is consequently reflected in the control quality, i.e. the deviation of the actual values of said variables (actual values) from the desired values (setpoint values).
A fundamental option of improving said control quality of the digital hydraulic valve resides in reducing the intervals between the dQ steps illustrated in FIG. 1B. These intervals can be reduced in the simplest manner by increasing the number of individual valves and thus increasing the number of dQ steps. However, this results in complex digital hydraulic valves that are not only expensive and voluminous but are also extremely susceptible to faults. As an alternative or in addition thereto, there is also the option of maintaining the through-flow openings in the individual valves in different magnitudes in order in this manner to come closer to a specific characteristic curve.
A control system of this type and also a method for controlling a consumer by means of a number of parallel-connected switching valves have been disclosed in the prior art, for example in accordance with WO 02/08 63 27 A1, wherein said valves are combined to form a digital hydraulic valve of this generic type and are digitally controlled.
On the basis of this prior art, the object of the present disclosure is to provide a digital hydraulic valve of this generic type that has a substantially continuous or almost continuous Q/V characteristic curve, but does not require the arrangement of a high number of individual valves.
This object is achieved by means of a digital hydraulic valve as described herein.